Solvent mediated surface engineering of α-Fe2O3 nanomaterials: facet sensitive energy storage materials

The surface chemical properties of iron oxide nanomaterials are keenly studied to explore their potential for many future applications. Therefore many synthetic strategies are now being pursued to develop unique morphologies with active surfaces and unusual crystal facets for advanced uses. Here, a novel process for the formation of an alpha-Fe2O3 phase has been established by a facile solvent mediated precipitation route. Ethylene glycol was used as the solvent and plays an active role in controlling the surface morphology and the orientation of facets during crystal growth. The effects of various parameters on the morphology, structure of the product, and electrochemical properties were studied. Mainly high surface energy facets were stabilized by a high concentration of EG in the reaction solution. The formation of (012) or (001) facets was observed in a reaction solution with a lower concentration of EG. Hematite with a flowery morphology and having (012) plane orientation was achieved by the assembly of pseudo cubes with (012) facets and a secondary growth process. The sample obtained at an Fe : EG ratio of 1 : 2 showed an ultrahigh pseudo capacitance value of 450 F g(-1) related to its high surface area. The present study can be further extended for the preparation of other functional oxides with new active facets for energy storage applications.